How deeply does Kubernetes in Action, Second Edition cover session affinity?

Explains layer boundaries, annotations, cookie naming, manifest configuration, and curl verification without developing controller internals.

Session affinity

As explained in Kubernetes in Action, Second Edition

Cookie-based session affinity is a traffic-routing policy that uses an HTTP cookie to keep a client associated with the same backend instance.

Session affinity keeps repeated requests from one client associated with the same backend instance. Cookie-based affinity does this with an HTTP cookie, so it requires an application-layer HTTP component rather than a transport-layer Service. section 12.4.1 section 11.1.3

Distinguish the two Kubernetes mechanisms:

A Service defaults to None, distributing connections without guaranteeing the destination pod; ClientIP instead keeps connections from one IP on the same pod for a configurable period. section 11.1.3
An Ingress operates at HTTP layer 7 and can read cookies, but its affinity annotations are specific to the chosen controller. section 12.4.1

Enable affinity in an Nginx Ingress

Add nginx.ingress.kubernetes.io/affinity: cookie to enable cookie routing and nginx.ingress.kubernetes.io/session-cookie-name: SESSION_COOKIE to choose the cookie name. An initial request returns Set-Cookie; send that value in a subsequent Cookie header, and repeated requests are forwarded to the same pod. section 12.4.1

$ kubectl exec -it quote-001 -c nginx -- sh
/ #

Use the manifest listing to inspect the complete networking.k8s.io/v1 Ingress configuration, including both affinity annotations. section 12.4.1

/ # curl http://10.96.136.190      #1
This is the quiz service running in pod quiz

/ # curl http://10.96.74.151       #2
This is the quote service running in pod quote-canary

Use the request listings to see the returned session cookie and replay it through the Cookie header. section 12.4.1

How Kubernetes in Action, Second Edition covers it

Cover of Kubernetes in Action, Second Edition

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Also explained in

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Learn Docker in a Month of Lunches, Second EditionA sticky session is session affinity that routes repeated requests from a client to the same service instance when possible.

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Related concepts

canary deploymentused by · A canary deployment is a release strategy that exposes a change to a limited portion of users, traffic, or infrastructure before expanding it more broadly.
serviceconfigures · A Kubernetes Service is an API resource that provides stable network access and service discovery for a changing set of Pods or other specified destinations.
statefulnessuses · Statefulness is the property of a system or operation whose behavior or results depend on information retained or changed across interactions or executions.
annotationconfigured by · A Kubernetes annotation is key-value metadata attached to an object for storing non-identifying descriptive, configuration, or operational information.
Traefikimplements · Traefik is an open-source dynamic reverse proxy and load balancer that configures routing using service discovery and runtime metadata.

This explainer was generated by Manning's knowledge graph from the text of Kubernetes in Action, Second Edition. The section links point to the parts of the book it draws on.